[llvm] [llvm][test][CGPluginTest] Fix missing `plugins` in test requirements (PR #215010)

[Seth Junot via llvm-commits]

xSetech wrote:

> No, but I'd like to get information on the exact conditions instead of just adding an extra condition.

That's interesting, but seems orthogonal to this change. I don't believe the dylib is _required_, but the original author of the test may have had their own reasons (or not) to over constrain when the test runs. I recommend reaching out to the original test author.

https://github.com/llvm/llvm-project/pull/215010